Brand new Weil McClain

Hows it going everyone, new to the page, ran across a new one for me, ive only been doing oil for a little over a year, so it's a brand new install, Weil McClain owb, installers called service in to help them tune the new system in because he had an issue with sane model last time, I ran a combustion analysis, and for the life of me, I could get my o2 readings down, I completely closed the shudder and air band and was still at like a 13% o2, I confirmed pump pressure, @ 140 per manufacturers specs. Low fire air baffle installed, draft at -.03, they had installed manufacturer supplied nozzle, I wanna say it was a .85 80b, I just couldn't get my readings down, could it be that the nozzle was just way to small? Why else would it lean out so much, any ideas would be greatly appreciated, im sure I'll be hearing more about it